Chromosome Number

Each species has a characteristic number of chromosomes. For species with genetically determined sexes, the haploid set is composed of autosomes plus a sex chromosome. Homo sapiens, for example, have 22 autosomes plus an X chromosome or Y chromosome. The haploid DNA content of chimpanzees is nearly identical, but is organized into 23 autosomes plus a sex chromosome.

The record for minimum number of chromosomes belongs to a subspecies of the ant, Myrmecia pilosula. The females have a single pair of chromosomes, while males have only a single chromosome. Like some other members of the insect class, these ants reproduce by a process called hap-lodiploidy, in which diploid fertilized eggs develop into females, while hap-loid unfertilized eggs develop into males.

The record for maximum number of chromosomes is found in the plant kingdom, due to a condition known as polyploidy. In polyploidy, many extra sets of chromosomes beyond the normal diploid number may accumulate haploid possessing only one copy of each chromosome base pairs two nucleotides (either DNA or RNA) linked by weak bonds autosomes chromosomes that are not sex determining (not X or Y)

Human Y and X chromosomes. These determine human gender.

over time. Cultivars of wheat exist with diploid numbers of chromosomes equaling 14, 28, or 42 (multiples of the haploid number, which is 7). Polyploids exist for many cultivated plants, including potatoes, strawberries, and cotton, as well as in wild plants such as dandelions. Polyploidy has led to striking numbers, and the known record is held by the fern Ophioglossum reticulatum, which has approximately 630 pairs.

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